There is no such thing as a more accurate cardiac ultrasound or electrocardiogram. They are different tests, and the clinic should choose the most appropriate test under the advice of the doctor.
Cardiac ultrasound is an imaging test, which mainly reflects whether there is any abnormality in the structure of the heart. Cardiac ultrasound can reflect whether the valves are narrowed or closed, whether the atria and ventricles are enlarged, and whether the walls of the ventricles and atria are thickened or defective. This test is recommended by your doctor if you suspect heart valve disease, cardiomyopathy, congenital heart disease, or pericardial disease.
Electrocardiogram (ECG) is mainly used to reflect the activity of the heart during the test and can be used as a preliminary diagnosis of arrhythmia, myocardial ischemia, myocardial infarction, and so on.
Cardiac ultrasound and electrocardiogram have more advantages and can be used together in a complementary manner. Therefore, it does not mean that cardiac ultrasound is more accurate than ECG.